The solution to your TOO FAST motor problems

Been eyeing these. Haven't tried them myself but they look to be just the ticket, especially for motor retrofits where the originals are no longer available and the new ones are too fast.

Pulse Width Modulated controllers are the best way to control your motor speed.

[ebay]300326881801[/ebay]

Sweet!!

Yeah .. a was thinking in bulding one of these using a micro.
But if you want real feedback (from RPM) you wil need a sensor installed somewhere (ej: the flywheel) to count the RPM or the time per revolution (it would be better). Without the feedbak, the speed will change as load changes.
Then of course some control strategy in the micro, but in general looks like the perfect solution for the speed problems getting the same RPM even when the load, temperature or voltage changes.
I think I'll do something in the future ...

Hey success.... I wish you success.

Seriously, if you do complete this project I would be very interested in seeing plans, schematics and implementation instructions on how you did it.

Please share with details....

~Norm.

I want to give it a try, only need a bit of time ... you know .
But it would be great to share ideas ... I'm stuck with the sensor .. do we need to intall one ?? and where ??

hey that looks like a great idea

SUCCESS said:

I want to give it a try, only need a bit of time ... you know .
But it would be great to share ideas ... I'm stuck with the sensor .. do we need to intall one ?? and where ??

Click to expand...

The device that I found does not require a sensor. It has a potentiometer that adjusts the speed by means of pulse width modulation. Instead of varying the voltage to the motor which would affect the torque (and also cause current consumption to jump up), it modulates the power fed to the motor by pulsing it and varying the pulse width. In other words, 1 second off, 1/2 second off etc etc until you get the speed you want. Since this isn't a feedback type of circuit it won't automatically adjust for differences in load. However, if the potentiometer is mounted in a convenient spot, you might think of it as a "pitch control." Rather than a band-aid, I guess you could say it's a "feature" or "upgrade."

Of course as you said earlier, a true feedback type of system would work best but I don't really think it's required unless we are talking really high end decks here. However, if you really want to implement feedback circuit into the design, I'm thinking that a an optical sensor would work great. The motor pulley would be the best place because it would be immune to belt slippage but the pulley is so small that it really isn't practical. The flywheel is a great spot and an optical sensor would probably be all you need. Perhaps paint the flywheel flat black and stick a reflective sticker on it along the edge...... none of which should alter the balance or torque required to operate the flywheel.

Of course, there might be one obstacle that might cause a wrinkle which we haven't considered. I've never disassembled one of these motors but often wondered how the speed can be so accurate and I'm thinking that these motors have a small speed controller built into them. So.... how will an internally speed controlled motor respond when the power fed to it is being pulse width modulated? Will it fight the modulation and continue to spin at the originally designed speed? If so, then it seems the only way to fix that would be to disable or remove the speed control from inside the motor.

or get a motor that uses the control outboard not in the motor itself that way it could be controled with the controller

monchito said:

or get a motor that uses the control outboard not in the motor itself that way it could be controled with the controller

Click to expand...

Agreed. Most cassette capstan motors I've seen are rated in terms of direction of rotation, voltage and speed (rpm). Would that mean the motor has a built in speed contoller programmed for that particular speed or would that mean that the speed is x-rpm at rated voltage?

Do you know of any sources for non-internally controlled motors?

superduper i think that those motors that have varible speed like the mabuchi 2000-4000 rpm which i have seen on some double decks might work they do not offer adjustment except on the main board which i might not be sure if its does have any adjustment well i open one of these there is a board but no adjustment could probably be maybe used with that controller , i had bought 2 of them from studioelectronics.com by mistake it uses 4 cables an a,b, +,- signs i but 9volts and i belive it was running at full speed that was 4000 rpm alvin chipmunks sounded better than what i was playing

Without feedback, PWM is like using a linear regulator (like the 317) ... of course with PWM, there's no power disipation in the semiconductor, and it's more efficient for battery life (the motor is not always on ...)

Once I tried to make an speed regulator for a walkman motor, with a variable output regulator ... You can get the thing working fine and adjusted ... but as I keep testing the speed went slow and slow. I adjust it and again the same.
Finally I realized that a fixed voltage isn't enough to keep RPM constant. Of course .. if you have an external pot, you move until you are pleased and you can update the adjust it in case you need. It would be nice some strobo to check that's adjusted ... like the turntables


Not sure but the common solution used in motors like mabuchi are a a variable voltage supply with some kind of correction using the sensed current. If current raises, that's because load had raisen. So more voltage is applied to the motor in order to keep the RPM constant. But motor manufacturers don't know the whole system (load, inercia ...) so this method isn't perfect. It's a big lay ... no real feedback ... but at least, current had been taken as a data. Hovewer, this babys had worked fine in our boomboxes ... cheap but still good.

I'll try to measure a mabuchi motor core voltage while changing the load .... That's an interesting homework !!!!


For those boomboxes with two speeds, I agree with Ramon. Take a motor without controller and put the controller in the main board.

Ok ... a motor with feedback is intended for high quality decks .. still love the idea though ....

Not to try to simplify this but, if I install and potentiometer on the power side of a motor and adjust is till it sounds right, will it work or not?

Just curious and seems there are several here with incredible smarts on the subject.

I'm a

Johnny, if you read back a few posts, I think you'll have an idea of what success and I said about this.

Motors with built in voltage regulators and speed adjustment can be dismantled. Inside you will find a small circuit board with the speed controler parts mounted on it. Also you will find the motor itself intact it can be seperated from this speed controler and wired directly. The speed controler circuit board could be used on other motors externally wired in applications where a regulated motor was not used as long as the voltage requitements are the sameas the motor from witch the regulator board was removed. Very easy to get externally adjustable speed on boomboxes that were not equipped with this type of motor.

That's interesting, BeverlyJean.

Excellent newbe post. Thanks for the info

Sorry for the resurrection, but using a feedback on the flywheel for active sensing sounds like a master idea. Does any cassette machine have that kind of speed sensing? Direct drive decks maybe, in some way.

This motor on Akai GXC 730D is the best I've seen on a cassette deck. I have two 730 decks and I love it!

https://www.ebay.com/itm/AKAI-GXC-730D-GXC-730-D-Cassette-Deck-Drive-Belt-Motor-Tape-Deck-Working-Motor/401497628508?hash=item5d7b1f9f5c:g:rHwAAOSwJwpakGYC

Brushless motor! It is an AC motor. The deck got motor speed control also.

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Interesting stuff .